pulseaudio: Add bbappend to disable gtk/x11

* we don't want gtk/libx11/.. to be pulled to image or even build even
  when we have x11 in DISTRO_FEATURES
* removing x11 from DISTRO_FEATURES is too strict as we plan to support
  some x11 apps later

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>